Recently, lithotrity apparatus for disintegrating calculus or kidney stones using high power pulsed ultrasonic wave (hereinafter referred to as ultrasonic shock wave) has attracted attention, because it has advantages in size and cost as compared to previous lithotrity apparatus of the type shown, for example, in U.S. Pat. No. 4,610,249, using other types of shock wave energy. A lithotrity using ultrasonic shock wave is shown, for example, in U.S. Pat. No. 4,617,931.
A lithotrity using ultrasonic shock wave, hereinafter referred to as an ultrasonic lithotrity, generally comprises a main ultrasonic transducer having a spherical surface with a focal point formed at its geometric center for disintegrating calculus, and an imaging ultrasonic transducer or other imaging device for generating a cross-sectional image of a patient, disposed at a distance from the main ultrasonic transducer. Once the focal point of the main ultrasonic transducer is positioned on the calculus using the image generated by the imaging transducer, a high power ultrasonic shock wave is transmitted to the calculus from the main ultrasonic transducer to destroy the calculus.
One problem with this apparatus is that it is extremely difficult to precisely locate the focal point of the main ultrasonic transducer on the calculus using only the cross-sectional image. Further, transmission of the high power ultrasonic shock wave must usually be repeated a number of times to completely disintegrate the calculus. Thus, even if the focal point is initially positioned at the calculus, the patient may move during the period between successive transmissions of high power shock wave so that the calculus is shifted away from the focal point. As a result, the high power shock wave may be directed toward, and, thus, harm neighboring normal human tissue.
The conventional apparatus depends on the eyesight of the operator to localize the focal point of the main transducer on the calculus, however, other apparatus exists which depends on the auditory sense of the operator. An example of this type of apparatus is shown in Japanese Patent Application (KOKAI) 62-49843. In operation, this apparatus first emits a weak ultrasonic shock wave from the main ultrasonic transducer. The weak ultrasonic shock wave is reflected by the calculus and the resulting echo signal is received back at the main ultrasonic transducer. A detector is provided which selectively detects only those echo signals that are reflected from areas near the focal point of the main ultrasonic transducer. The selected echo signals are then supplied to a loudspeaker which converts the signals into audible sound, so that the operator can then adjust the focal point of the main ultrasonic transducer to the calculus, where the sound is greatest.
This apparatus, however, has several disadvantages. First, because the main ultrasonic transducer must emit both high power and weak ultrasonic shock waves, and also receive echo signals corresponding to the weak ultrasonic shock wave, the apparatus is complicated and large in size. Further, like previous devices, the apparatus depends upon the operator to precisely locate the focal point of the main transducer at the position of the calculus.